PWM power amplifier

• US 6,473,009 B2
• Filed: 08/03/2001
• Issued: 10/29/2002
• Est. Priority Date: 08/04/2000
• Status: Expired due to Term

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Botti, Edoardo, Grosso, Antonio
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Mai, Lam T.
• Application Number:
  US09/921,643
• Publication Number:
  US 20020036579A1
• Time in Patent Office: 452 Days
• Field of Search: 341/144, 341/152, 341/172, 341/102, 330/250, 330/251, 330/252, 330/262, 375/238, 375/242
• US Class Current: 341/102
• CPC Class Codes: G06F 1/025 for functions having two-valued amplitude, e.g. Walsh functions
• CPC Class Codes: H03F 2200/342 Pulse code modulation being used in an amplifying circuit
• CPC Class Codes: H03F 2200/351 Pulse width modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H03M 1/825 by comparing the input signal with a digital ramp signal

Abstract

A PWM power amplifier having at least one PCM/PWM converter fed by PCM digital input signals and producing PWM digital output signals, and at least one power amplification final stage of the PWM digital output signals. At least one PCM/PWM converterincludes a counter fed with at least one clock signal produced by a clock generator device and having a digital comparator suitable for comparing the PCM digital input signals of at least one PCM/PWM converter with a digital comparison signal produced by the counter and producing in output the PWM digital signals. The clock generator device includes a pulse generator device and an oscillator; the pulse generator device receives a signal at a frequency that is equal to the frequency of the PCM digital input signals of the at least one PCM/PWM converter and produces in output reset pulses. The reset pulses are sent in input to the oscillator, which produces in output the at least one clock signal.

Claims

1. A PWM power amplifier, comprising:

at least one PCM/PWM converter which is fed by PCM digital input signals and produces PWM digital output signals, and at least one final stage of power amplification of the PWM digital signals in output from said at least one PCM/PWM converter, said at least one PCM/PWM converter comprising a counter fed with at least one clock signal produced by a clock generator device and comprising a digital comparator suitable for comparing said PCM digital input signals of said at least one PCM/PWM converter with a digital comparison signal produced by said counter and producing in output said PWM digital signals, said clock generator device comprising a pulse generator device and an oscillator, said pulse generator device receiving a signal at a frequency equal to the frequency of said PCM digital input signals of said at least one PCM/PWM converter and producing in output reset pulses, said reset pulses being sent in input to said oscillator producing in output said at least one clock signal.

2. The amplifier of claim 1, comprising an oversampling and noise shaping block receiving first PCM digital input signals organized in words with a given number of bits and at a given frequency and producing in output second PCM digital signals organized in words composed of a number of bits lower than said given number of bits and at a multiple frequency with respect to said given frequency of the first PCM digital input signals, said second PCM digital signals being the PCM digital signals in input to said at least one PCM/PWM converter.

3. The amplifier of claim 2, comprising a first bus suitable for transmitting first digital data PCM containing a first number of more significant bits of said second PCM digital signals and a second bus suitable for transmitting second PCM digital data containing a second number of less significant bits of said second PCM digital signals, and comprising a first and a second PCM/PWM converter fed respectively by said first and second PCM digital data and producing in output respectively a first and a second PWM signal.

4. The amplifier of claim 3 wherein said second signal PWM is previously attenuated by a ratio equivalent to the power in base two of the second number of less significant bits transmitted by said second bus to the input of said second PCM/PWM converter and is summed to said first signal PWM at an inverting node of said at least one power amplification final stage of the amplifier.

5. The amplifier of claim 1 wherein said at least one clock generator produces a clock signal whose frequency equals the product of the frequency of the bits of the PCM digital signals in input to said at least one PCM/PWM converter by the power in base two of the number of bits of said PCM digital signals in input to at least one PCM/PWM converter, said counter fed by said at least one clock signal generating a digital comparison output signal composed of said number of bits in the form of at least one ramp of digital values at an identical or halved frequency compared to said frequency of bits of the PCM digital signals in input to the at least one PCM/PWM converter.

6. The amplifier of claim 5 wherein said digital comparison signal of said at least one PCM/PWM converter is in the form of a succession of upward ramps of digital values at a frequency identical to said frequency of bits of the PCM digital signals in input to at least one PCM/PWM converter.

7. The amplifier of claim 5 wherein said at least one PCM/PWM converter is a double ramp type, said counter being of the up/down type, having in input a ramp inversion signal and generating in output a digital comparison signal composed by the number of bits of said PCM digital signals in input to at least one PCM/PWM converter under the form of a succession of up and down ramps at a halved frequency compared to the frequency of the PCM digital signals in input to said at least one PCM/PWM converter.

8. The amplifier of claim 1, comprising a single power amplification final stage.

9. The amplifier of claim 1, comprising two identical power amplification final stages functioning in counterphase and in which the inversion of the signal fed to the inverting input of said two final stages is made by inverting the PWM digital signal in output from said at least one PCM/PWM converter.

10. The amplifier of claim 1, comprising two identical power amplification final stages functioning in counterphase and in which the inversion of the signal fed to the inverting input of said two final stages is made by duplicating said at least one PCM/PWM converter and inverting the PCM digital signals in input to said at least two PCM/PWM converters.

11. The amplifier of claim 1 wherein said clock generator produces a clock signal whose frequency equals the product of the frequency of the bits of the PCM digital signals in input to said at least one PCM/PWM converter by the power in base two of the number of bits of said PCM digital signals in input to at least one PCM/PWM converter, said at least one PCM/PWM converter is a double ramp type, said counter being fed by said clock signal and being the up/down type, having in input a ramp inversion signal and generating in output a digital comparison signal composed of the number of bits of said PCM digital signals in input to at least one PCM/PWM converter in the form of a succession of up and down ramps at a halved frequency compared to the frequency of the PCM digital signals in input to said at least one PCM/PWM converter, and comprising two identical power amplification final stages functioning in counterphase and in which the inversion of the signal fed to the inverting input of said two final stages is made by duplicating said at least one PCM/PWM double ramp converter and inverting the ramp inversion signal of said at least one PCM/PWM converter and feeding both said at least one PCM/PWM converter and its duplicate with the same PCM input digital signals.

12. The amplifier of claim 4 wherein said at least one clock generator produces a clock signal whose frequency equals the product of the frequency of the bits of the PCM digital signals in input to said at least one PCM/PWM converter by the power in base two of the number of bits of said PCM digital signals in input to at least one PCM/PWM converter, said at least one PCM/PWM converter being double ramp type, said counter being fed by said clock signal and being the up/down type, having in input a ramp inversion signal and generating in output a digital comparison signal composed of the number of bits of said PCM digital signals in input to at least one PCM/PWM converter in the form of a succession of up and down ramps at a halved frequency compared to the frequency of the PCM digital signals in input to said at least one PCM/PWM converter;

and comprising two identical power amplification final stages functioning in counterphase and in which the inversion of the signal fed to the inverting input of said two final stages is made by duplicating said couple of PCM/PWM double ramp converters and inverting the signal of ramp inversion of said couple of PCM/PWM converters and feeding both said couple of PCM/PWM converters and their duplicate with the same PCM digital signals of said first bus and of said second bus.

13. The amplifier of claim 12, comprising means for inverting the PWM signals produced at the output of the PCM/PWM converters of said couple and its duplicate which are fed with said PCM digital signals containing the less significant bits, means for attenuating the inverted PWM signals and means for summing each of said PWM signals inverted and attenuated on the inverting node on which the PWM signals produced by the PCM/PWM converters belonging to the other one between said couple of converters or its duplicate are summed.

14. The amplifier of claim 1 wherein said oscillator comprises inverters each formed by a couple of MOS transistors and placed in series and in a loop so that the input of the first of said inverters is connected with the output of the last of said inverters, capacities in a number equal to that of the inverters and each one having a terminal connected to a respective input of each inverter and the other terminal grounded, a transistor MOS having in input said reset pulses and the output connected to the input of said first inverter.

15. A PWM power amplifier, comprising:

a digital signal circuit configured to receive in input a PCM signal with M bits and to convert the PCM signal with oversampling and noise shaping techniques into a PCM digital signal having N bits, where M>

N;

first and second PCM/PWM converters coupled to the digital signal circuit, the converters comprising a counter and a comparator, the counter configured to receive a clock signal and to generate a digital comparison signal, and the comparator configured to receive the digital comparison signal and at least a portion of the PCM digital signal and to generate first and second PWM digital signals as output of the first and second PCM/PWM converters, respectively;

a clock generator circuit comprising a pulse generator device and an oscillator, the pulse generator device receiving a signal at a frequency equal to a frequency of the PCM signal and to generate output reset pulses, and an oscillator configured to receive the output reset pulses and to generate the clock signal; and

a final stage configured to receive a combination of the first and second PWM digital signals and to provide power amplification thereof in an output.

16. The amplifier of claim 15, wherein the digital signal circuit comprises an oversampling and noise shaping block configured to receive the PCM signal in words with a predetermined number of M bits at an input frequency and to generate the PCM digital signal organized in words composed of N number of bits at a second frequency that is a multiple of the first frequency.

17. The amplifier of claim 16, wherein the second PWM digital signal output by the second PCM/PWM converter is attenuated by a ratio equivalent to the power in base two of the number of bits in the portion of the PCM digital signal received by the second PCM/PWM converter, and wherein the first and second PWM digital signals are summed at an input of the final stage.

18. A PWM power amplifier, comprising:

a digital signal circuit configured to receive in input a PCM signal with M bits and to convert the PCM signal with oversampling and noise shaping techniques into a PCM digital signal having N bits, where M>

N;

first and second PCM/PWM converters coupled to the digital signal circuit, the converters comprising a counter and a comparator, the counter configured to receive a clock signal and to generate a digital comparison signal, and the comparator configured to receive the digital comparison signal and at least a portion of the PCM digital signal and to generate first and second PWM digital signals as output of the first and second PCM/PWM converters, respectively;

a clock generator circuit comprising a pulse generator device and an oscillator, the pulse generator device receiving a signal at a frequency equal to a frequency of the PCM signal and to generate output reset pulses, and an oscillator configured to receive the output reset pulses and to generate the clock signal, the clock signal having a clock frequency equal to the product of the first frequency by the power in base two of the number of bits of the PCM signal portion input into one of the first and second PCM/PWM converters, the counter receiving the clock signal and configured to generate the digital comparison output signal in the form of at least one ramp of digital values at an identical or halved frequency compared to the first frequency; and

a final stage configured to receive a combination of the first and second PWM digital signals and to provide power amplification thereof in an output.

19. A PWM power amplifier, comprising:

a digital signal circuit configured to receive in input a PCM signal with M bits and to convert the PCM signal with oversampling and noise shaping techniques into a PCM digital signal having N bits, where M>

N;

first and second PCM/PWM converters coupled to the digital signal circuit, the converters comprising a counter and a comparator, the counter configured to receive a clock signal and to generate a digital comparison signal, and the comparator configured to receive the digital comparison signal and at least a portion of the PCM digital signal and to generate first and second PWM digital signals as output of the first and second PCM/PWM converters, respectively;

a clock generator circuit comprising a pulse generator device and an oscillator, the pulse generator device receiving a signal at a first frequency equal to a frequency of the PCM signal and to generate output reset pulses, and an oscillator configured to receive the output reset pulses and to generate the clock signal, the clock signal having a frequency equal to the product of the first frequency by the power in base two of the number of bits of the PCM signal received by one of the first and second PCM/PWM converters, each of the first and second PCM/PWM converters comprising a double ramp type converter receiving the clock signal, and each counter being of the up/down type and having in input a ramp conversion signal and configured to generate in output the digital comparison signal comprising the number of bits of the portion of the PCM signal received by the respective counter, and further in the form of a succession of up and down ramps at a halved frequency of the first frequency; and

a first final stage configured to receive a combination of the first and second PWM digital signals and to provide power amplification thereof in an output, and a second final stage that is a duplicate of the first final stage and functioning in counter phase thereof and having an inversion signal input that receives an inversion of a combination of the PWM digital signals that is generated by a second and third pair of PCM/PWM double ramp converters that are duplicates of the first and second PCM/PWM converters and having the ramp inversion signal inverted and to generate a power amplification thereof.